A solid-state imaging device such as a CCD image sensor and a CMOS image sensor is used for various purposes in, for example, a digital still camera, a video camera, or a security camera. Recently, a single-chip image sensor that acquires items of color information through a single pixel array has been in wide use.
In the image sensor, a photodiode is formed by using, for example, an N-type impurity layer which is formed in a P-type semiconductor substrate (or semiconductor region). The N-type impurity layer of the photodiode is formed so that its impurity concentration has a relatively uniform in-plane distribution. The whole impurity concentration of the N-type impurity layer is increased (made higher) so that the photodiode can store a predetermined amount of charge.
A P-type impurity layer is formed in the semiconductor substrate around the N-type impurity layer of the photodiode for inter-pixel element isolation. The potential distribution of the N-type impurity layer gently grows deeper from the periphery of the N-type impurity layer toward its center because of the P-type impurity layer. Therefore, the amount of charge that can be stored in the peripheral part of the N-type impurity layer is less than the amount of charge that can be stored in the central part of the N-type impurity diffusion layer.